I was in need of a thin spacer for my noiseblocker fans .
The fan blades slightly touched the case creating a quite noisy rattling sound.

I asked chatgpt to create a model for a fan spacer and tweaked the script a little. 
The attached STL fits my 50mm fan. Download OpenSCAD to create a custom one or drop a comment with details. I'll try to create a fitting STL asap :)

I am using this design to mount 4xNB-BlackSilentFan 50mm on the front grill of a Inter-Tech-2u-2404S 2U server case. I got 2 40mm fans in the back pushing air out, so it was necessary to rotate the 50mm fans such that these pull fresh air into the case.